Why Visitors to Ladakh Get Breathless Even When They Are Standing Still
Follow oxygen and carbon dioxide as blood carries them between the lungs and the tissues, separate breathing from tissue respiration and see where body heat comes from, compare anaerobic respiration in yeast and in human muscles, and understand breathlessness at high altitude, hypoxia and asphyxiation.
What happens to oxygen after it enters the blood?
Part 1 followed air as far as the alveoli, where oxygen crosses into the blood. That is only the beginning of oxygen's journey. It must now be carried through the blood to every cell in the body, used inside those cells to release energy from food, and replaced by carbon dioxide, which travels back to the lungs.
This part follows that journey and what happens when it fails.
- Transport — how haemoglobin carries oxygen, and how carbon dioxide is carried back
- Tissue respiration — the chemical process in cells that releases energy, and why it also produces body heat
- Anaerobic respiration — what happens when there is not enough oxygen, in yeast and plants and in human muscles
- High altitude, hypoxia and asphyxiation — what happens when the body cannot get enough oxygen
Why visitors to Ladakh feel it. Tourists arriving in Leh are advised to rest for their first day or two, because even walking up a flight of stairs can leave them gasping. The air there contains the same proportion of oxygen as air at sea level, but it is thinner — at lower pressure — so each breath delivers fewer oxygen molecules. The body has to work harder to get the oxygen it needs.
Two ideas must be kept apart throughout.
- Breathing is the physical movement of air in and out of the lungs
- Respiration, in the cells, is the chemical breakdown of food to release energy
They depend on each other — breathing supplies the oxygen that cellular respiration uses, and removes the carbon dioxide it produces — but they are not the same process, and the difference is examined in this chapter.
The link to earlier chapters. The glucose made by photosynthesis is the fuel burned in respiration, and the carbon dioxide released returns to the air to be used by plants again — the two halves of the carbon cycle meeting inside your body.
This page covers the second part of the ICSE Class 10 Biology chapter on the respiratory system: transport of gases, breathing and tissue respiration, anaerobic respiration, and the effects of oxygen shortage.
This part follows that journey and what happens when it fails.
- Transport — how haemoglobin carries oxygen, and how carbon dioxide is carried back
- Tissue respiration — the chemical process in cells that releases energy, and why it also produces body heat
- Anaerobic respiration — what happens when there is not enough oxygen, in yeast and plants and in human muscles
- High altitude, hypoxia and asphyxiation — what happens when the body cannot get enough oxygen
Why visitors to Ladakh feel it. Tourists arriving in Leh are advised to rest for their first day or two, because even walking up a flight of stairs can leave them gasping. The air there contains the same proportion of oxygen as air at sea level, but it is thinner — at lower pressure — so each breath delivers fewer oxygen molecules. The body has to work harder to get the oxygen it needs.
Two ideas must be kept apart throughout.
- Breathing is the physical movement of air in and out of the lungs
- Respiration, in the cells, is the chemical breakdown of food to release energy
They depend on each other — breathing supplies the oxygen that cellular respiration uses, and removes the carbon dioxide it produces — but they are not the same process, and the difference is examined in this chapter.
The link to earlier chapters. The glucose made by photosynthesis is the fuel burned in respiration, and the carbon dioxide released returns to the air to be used by plants again — the two halves of the carbon cycle meeting inside your body.
This page covers the second part of the ICSE Class 10 Biology chapter on the respiratory system: transport of gases, breathing and tissue respiration, anaerobic respiration, and the effects of oxygen shortage.
How does blood carry oxygen and carbon dioxide between the lungs and the tissues?
Oxygen is carried mainly by haemoglobin in red blood cells, which picks it up in the lungs and releases it in the tissues; carbon dioxide is carried back mostly as hydrogen carbonate ions in the plasma, partly bound to haemoglobin and partly dissolved.
1. Transport of oxygen.
- **About of the oxygen in blood is carried by haemoglobin in the red blood cells
- About is dissolved in the plasma
In the lungs, where oxygen is plentiful, haemoglobin combines with oxygen to form oxyhaemoglobin**, which makes the blood bright red:
In the tissues, where oxygen is scarce, oxyhaemoglobin releases its oxygen, which diffuses into the cells:
Each haemoglobin molecule can carry up to four oxygen molecules, which is why so much oxygen travels in so little blood.
2. Transport of carbon dioxide. Carbon dioxide made in the tissues diffuses into the blood and is carried in three ways:
- Mostly as hydrogen carbonate ions in the plasma — carbon dioxide reacts with water inside red blood cells, speeded up by an enzyme, carbonic anhydrase:
- Partly combined with haemoglobin, as carbaminohaemoglobin
- A small amount dissolved directly in the plasma
In the lungs, these reactions reverse, carbon dioxide is released into the alveoli, and it is breathed out.
Worked example — oxygen delivered. Every of oxygenated blood typically gives up about of oxygen to the tissues at rest. How much oxygen is delivered by of blood passing through the tissues?
Worked check — the hydrogen carbonate reaction balances.
- Carbon: ; oxygen: on the left, in
- Hydrogen: on the left; on the right
- Charge: on the left; on the right
Balanced.
An everyday example — the danger of carbon monoxide. Carbon monoxide from a faulty gas heater or a charcoal stove in a closed room combines with haemoglobin far more strongly than oxygen does, forming carboxyhaemoglobin. The haemoglobin can then no longer carry oxygen, so the tissues starve even though the person is still breathing — which is why such fumes are so dangerous.
The boundary case. Oxygen is loaded where it is plentiful and unloaded where it is scarce — by the same haemoglobin. Haemoglobin does not decide where to deliver oxygen; the difference in oxygen concentration between lungs and tissues does, which is why active tissues, using oxygen fastest, receive the most.
1. Transport of oxygen.
- **About of the oxygen in blood is carried by haemoglobin in the red blood cells
- About is dissolved in the plasma
In the lungs, where oxygen is plentiful, haemoglobin combines with oxygen to form oxyhaemoglobin**, which makes the blood bright red:
In the tissues, where oxygen is scarce, oxyhaemoglobin releases its oxygen, which diffuses into the cells:
Each haemoglobin molecule can carry up to four oxygen molecules, which is why so much oxygen travels in so little blood.
2. Transport of carbon dioxide. Carbon dioxide made in the tissues diffuses into the blood and is carried in three ways:
- Mostly as hydrogen carbonate ions in the plasma — carbon dioxide reacts with water inside red blood cells, speeded up by an enzyme, carbonic anhydrase:
- Partly combined with haemoglobin, as carbaminohaemoglobin
- A small amount dissolved directly in the plasma
In the lungs, these reactions reverse, carbon dioxide is released into the alveoli, and it is breathed out.
Worked example — oxygen delivered. Every of oxygenated blood typically gives up about of oxygen to the tissues at rest. How much oxygen is delivered by of blood passing through the tissues?
Worked check — the hydrogen carbonate reaction balances.
- Carbon: ; oxygen: on the left, in
- Hydrogen: on the left; on the right
- Charge: on the left; on the right
Balanced.
An everyday example — the danger of carbon monoxide. Carbon monoxide from a faulty gas heater or a charcoal stove in a closed room combines with haemoglobin far more strongly than oxygen does, forming carboxyhaemoglobin. The haemoglobin can then no longer carry oxygen, so the tissues starve even though the person is still breathing — which is why such fumes are so dangerous.
The boundary case. Oxygen is loaded where it is plentiful and unloaded where it is scarce — by the same haemoglobin. Haemoglobin does not decide where to deliver oxygen; the difference in oxygen concentration between lungs and tissues does, which is why active tissues, using oxygen fastest, receive the most.
How is breathing different from tissue respiration, and why does respiration produce heat?
Breathing is the physical movement of air in and out of the lungs, while tissue respiration is the chemical oxidation of food inside cells that releases energy; only part of that energy is stored in ATP, and the rest is released as heat that keeps the body warm.
Breathing versus tissue respiration:
- Nature: breathing — a physical process; tissue respiration — a biochemical process
- Where: breathing — in the lungs and air passages; respiration — inside every living cell, in the cytoplasm and mitochondria
- What happens: breathing — air is moved in and out; respiration — glucose is broken down
- Energy: breathing — uses energy for muscle movement; respiration — releases energy
- Enzymes: breathing — not involved; respiration — many enzymes control each step
The equation for aerobic tissue respiration:
External and internal respiration.
- External respiration — exchange of gases between alveolar air and blood in the lungs
- Internal respiration — exchange of gases between blood and body cells in the tissues
- Cellular respiration — the chemical breakdown of glucose within the cells
Why respiration produces heat. The energy in glucose is not transferred perfectly into ATP. A large part of it escapes as heat at each step. In birds and mammals, this heat keeps the body at a steady warm temperature, which is why a person's body stays warm even on a cool day.
Worked example — how much energy becomes heat? Using textbook values, the complete oxidation of mole of glucose releases about , and aerobic respiration forms about ATP, each storing about . Estimate the percentage stored as ATP.
**So roughly of the energy is released as heat — the body's own central heating.
Worked check — the respiration equation balances.
- Carbon**:
- Hydrogen: on the left; on the right
- Oxygen: on the left; on the right
Balanced.
An everyday example. After a fast game of kabaddi or a run around the school ground, you feel hot and start to sweat. Your muscles are respiring rapidly to supply energy, and the extra heat released by that respiration raises your body temperature until sweating cools you down.
The boundary case. Plants respire too, all the time, even though they do not breathe with lungs. Respiration is universal in living cells; breathing is a feature only of animals with a breathing system — which is why the two words cannot be used as if they meant the same thing.
Breathing versus tissue respiration:
- Nature: breathing — a physical process; tissue respiration — a biochemical process
- Where: breathing — in the lungs and air passages; respiration — inside every living cell, in the cytoplasm and mitochondria
- What happens: breathing — air is moved in and out; respiration — glucose is broken down
- Energy: breathing — uses energy for muscle movement; respiration — releases energy
- Enzymes: breathing — not involved; respiration — many enzymes control each step
The equation for aerobic tissue respiration:
External and internal respiration.
- External respiration — exchange of gases between alveolar air and blood in the lungs
- Internal respiration — exchange of gases between blood and body cells in the tissues
- Cellular respiration — the chemical breakdown of glucose within the cells
Why respiration produces heat. The energy in glucose is not transferred perfectly into ATP. A large part of it escapes as heat at each step. In birds and mammals, this heat keeps the body at a steady warm temperature, which is why a person's body stays warm even on a cool day.
Worked example — how much energy becomes heat? Using textbook values, the complete oxidation of mole of glucose releases about , and aerobic respiration forms about ATP, each storing about . Estimate the percentage stored as ATP.
**So roughly of the energy is released as heat — the body's own central heating.
Worked check — the respiration equation balances.
- Carbon**:
- Hydrogen: on the left; on the right
- Oxygen: on the left; on the right
Balanced.
An everyday example. After a fast game of kabaddi or a run around the school ground, you feel hot and start to sweat. Your muscles are respiring rapidly to supply energy, and the extra heat released by that respiration raises your body temperature until sweating cools you down.
The boundary case. Plants respire too, all the time, even though they do not breathe with lungs. Respiration is universal in living cells; breathing is a feature only of animals with a breathing system — which is why the two words cannot be used as if they meant the same thing.
How does anaerobic respiration in plants differ from anaerobic respiration in humans?
Without enough oxygen, yeast and some plant tissues break glucose down into ethanol and carbon dioxide, while human muscle cells break it down into lactic acid with no carbon dioxide; both release far less energy than aerobic respiration.
Anaerobic respiration is the breakdown of glucose without oxygen, releasing a small amount of energy.
1. In yeast and plants — alcoholic fermentation.
- Products: ethanol and carbon dioxide
- Occurs in: yeast, and in plant tissues such as roots in waterlogged soil and some germinating seeds when oxygen is short
2. In human muscles — lactic acid formation.
- Product: lactic acid only — no carbon dioxide
- Occurs in: skeletal muscles during vigorous exercise, when oxygen cannot be supplied fast enough
Comparing the two:
- Products: plants — ethanol and CO2; humans — lactic acid
- Carbon dioxide released: plants — yes; humans — no
- Energy: both release **only about ATP per glucose
- Where: plants — yeast, waterlogged roots; humans — overworked muscles
Worked example — comparing energy yields.** Aerobic respiration gives about ATP per glucose; anaerobic respiration gives about . How many times more energy does aerobic respiration release?
Worked check — the lactic acid equation balances.
- Carbon: on the left; on the right
- Hydrogen: on the left; on the right
- Oxygen: on the left; on the right
Balanced.
Oxygen debt and muscle fatigue.
- Lactic acid building up in muscles causes fatigue and cramps
- After exercise, you keep breathing hard to supply extra oxygen that converts the lactic acid — the oxygen debt is being repaid
- Much of the lactic acid is carried to the liver, where it is converted back to useful compounds
An everyday example. Batter for idli and dosa, left overnight, rises and turns slightly sour. Microbes in the batter break down its sugars without oxygen, producing carbon dioxide that makes it fluffy and acids that give the sour taste — anaerobic respiration at work in the kitchen.
The boundary case. Anaerobic respiration is an emergency backup in human muscle, not a way of life. The brain cannot rely on it at all, which is why a shortage of oxygen affects the brain first and most seriously — the subject of the next section.
Anaerobic respiration is the breakdown of glucose without oxygen, releasing a small amount of energy.
1. In yeast and plants — alcoholic fermentation.
- Products: ethanol and carbon dioxide
- Occurs in: yeast, and in plant tissues such as roots in waterlogged soil and some germinating seeds when oxygen is short
2. In human muscles — lactic acid formation.
- Product: lactic acid only — no carbon dioxide
- Occurs in: skeletal muscles during vigorous exercise, when oxygen cannot be supplied fast enough
Comparing the two:
- Products: plants — ethanol and CO2; humans — lactic acid
- Carbon dioxide released: plants — yes; humans — no
- Energy: both release **only about ATP per glucose
- Where: plants — yeast, waterlogged roots; humans — overworked muscles
Worked example — comparing energy yields.** Aerobic respiration gives about ATP per glucose; anaerobic respiration gives about . How many times more energy does aerobic respiration release?
Worked check — the lactic acid equation balances.
- Carbon: on the left; on the right
- Hydrogen: on the left; on the right
- Oxygen: on the left; on the right
Balanced.
Oxygen debt and muscle fatigue.
- Lactic acid building up in muscles causes fatigue and cramps
- After exercise, you keep breathing hard to supply extra oxygen that converts the lactic acid — the oxygen debt is being repaid
- Much of the lactic acid is carried to the liver, where it is converted back to useful compounds
An everyday example. Batter for idli and dosa, left overnight, rises and turns slightly sour. Microbes in the batter break down its sugars without oxygen, producing carbon dioxide that makes it fluffy and acids that give the sour taste — anaerobic respiration at work in the kitchen.
The boundary case. Anaerobic respiration is an emergency backup in human muscle, not a way of life. The brain cannot rely on it at all, which is why a shortage of oxygen affects the brain first and most seriously — the subject of the next section.
Why is breathing difficult at high altitude, and what are hypoxia and asphyxiation?
At high altitude the air pressure is lower, so each breath carries fewer oxygen molecules and the body breathes faster and deeper to compensate; hypoxia is a shortage of oxygen reaching the tissues, and asphyxiation is suffocation caused by oxygen being cut off from the body.
1. The effect of high altitude.
- The proportion of oxygen in the air is the same at high altitude as at sea level
- But the air pressure is lower, so a lungful of air contains fewer oxygen molecules
- Less oxygen diffuses into the blood with each breath
The body's immediate responses:
- Faster and deeper breathing, to take in more air
- A faster heart rate, to circulate the available oxygen more quickly
Over days and weeks — acclimatisation:
- The body makes more red blood cells and more haemoglobin, so the blood can carry more oxygen
- Breathing and circulation settle as the body adjusts
If the ascent is too fast, a person may suffer altitude sickness — headache, nausea, dizziness and breathlessness.
Worked example — breathing to keep up. At rest at sea level a person breathes of air per minute. At a high altitude where the air pressure is about half that at sea level, each litre holds about half as many oxygen molecules. How much air per minute would be needed to take in the same amount of oxygen?
The person would need to move twice as much air — which is why breathing becomes fast and laboured.
2. Hypoxia. Hypoxia is a condition in which the tissues do not receive enough oxygen. Causes include:
- Low oxygen in the air, as at high altitude
- Carbon monoxide poisoning, which blocks haemoglobin
- Too little haemoglobin, as in severe anaemia
- Poor circulation, so blood does not reach the tissues
3. Asphyxiation. Asphyxiation is suffocation — a severe shortage of oxygen reaching the body, together with a build-up of carbon dioxide, caused when breathing is prevented. Causes include:
- Blockage of the air passages, as by choking on food
- Drowning
- Strangulation or smothering
- Breathing an atmosphere without oxygen, such as dense smoke
If not corrected quickly, asphyxiation leads to unconsciousness and death, because the brain cannot survive long without oxygen.
An everyday example. Soldiers and mountaineers going to very high posts and peaks in the Himalayas climb in stages, spending days at intermediate heights. This gives the body time to acclimatise by producing more red blood cells before going higher.
The boundary case — the misconception about mountain air. Air on a mountain is not low in oxygen because the gas has been used up. It has the same proportion of oxygen; it is simply less dense, so the same volume holds fewer molecules of every gas.
1. The effect of high altitude.
- The proportion of oxygen in the air is the same at high altitude as at sea level
- But the air pressure is lower, so a lungful of air contains fewer oxygen molecules
- Less oxygen diffuses into the blood with each breath
The body's immediate responses:
- Faster and deeper breathing, to take in more air
- A faster heart rate, to circulate the available oxygen more quickly
Over days and weeks — acclimatisation:
- The body makes more red blood cells and more haemoglobin, so the blood can carry more oxygen
- Breathing and circulation settle as the body adjusts
If the ascent is too fast, a person may suffer altitude sickness — headache, nausea, dizziness and breathlessness.
Worked example — breathing to keep up. At rest at sea level a person breathes of air per minute. At a high altitude where the air pressure is about half that at sea level, each litre holds about half as many oxygen molecules. How much air per minute would be needed to take in the same amount of oxygen?
The person would need to move twice as much air — which is why breathing becomes fast and laboured.
2. Hypoxia. Hypoxia is a condition in which the tissues do not receive enough oxygen. Causes include:
- Low oxygen in the air, as at high altitude
- Carbon monoxide poisoning, which blocks haemoglobin
- Too little haemoglobin, as in severe anaemia
- Poor circulation, so blood does not reach the tissues
3. Asphyxiation. Asphyxiation is suffocation — a severe shortage of oxygen reaching the body, together with a build-up of carbon dioxide, caused when breathing is prevented. Causes include:
- Blockage of the air passages, as by choking on food
- Drowning
- Strangulation or smothering
- Breathing an atmosphere without oxygen, such as dense smoke
If not corrected quickly, asphyxiation leads to unconsciousness and death, because the brain cannot survive long without oxygen.
An everyday example. Soldiers and mountaineers going to very high posts and peaks in the Himalayas climb in stages, spending days at intermediate heights. This gives the body time to acclimatise by producing more red blood cells before going higher.
The boundary case — the misconception about mountain air. Air on a mountain is not low in oxygen because the gas has been used up. It has the same proportion of oxygen; it is simply less dense, so the same volume holds fewer molecules of every gas.
Exam tip
What earns full marks on gas transport, respiration and oxygen shortage?
Name the carrier and the chemical form for each gas, compare breathing and respiration point by point, write both anaerobic equations with products named, and define hypoxia and asphyxiation separately.
- Oxygen: carried mainly by haemoglobin as oxyhaemoglobin; a little dissolved in plasma
- Carbon dioxide: carried mainly as hydrogen carbonate ions, partly as carbaminohaemoglobin, a little dissolved
- Mention carbonic anhydrase in red blood cells
- Explain carbon monoxide poisoning through carboxyhaemoglobin
- Compare breathing and respiration on nature, site, energy and enzymes
- Write the aerobic respiration equation, balanced, with energy
- Explain heat production — only part of the energy is stored in ATP
- Write alcoholic fermentation and lactic acid formation with products, and state that muscle anaerobic respiration releases no CO2
- Explain oxygen debt and muscle fatigue
- For high altitude, say low pressure, not low proportion of oxygen, and describe faster breathing and more red blood cells
The misconception to name. Breathing and respiration are not the same process. Breathing moves air; respiration releases energy from food in cells. Using respiration to mean breathing in an answer that compares them loses the definition marks.
A second trap. Writing carbon dioxide as a product of anaerobic respiration in human muscles. Muscle cells produce only lactic acid; carbon dioxide is released only in alcoholic fermentation.
- Oxygen: carried mainly by haemoglobin as oxyhaemoglobin; a little dissolved in plasma
- Carbon dioxide: carried mainly as hydrogen carbonate ions, partly as carbaminohaemoglobin, a little dissolved
- Mention carbonic anhydrase in red blood cells
- Explain carbon monoxide poisoning through carboxyhaemoglobin
- Compare breathing and respiration on nature, site, energy and enzymes
- Write the aerobic respiration equation, balanced, with energy
- Explain heat production — only part of the energy is stored in ATP
- Write alcoholic fermentation and lactic acid formation with products, and state that muscle anaerobic respiration releases no CO2
- Explain oxygen debt and muscle fatigue
- For high altitude, say low pressure, not low proportion of oxygen, and describe faster breathing and more red blood cells
The misconception to name. Breathing and respiration are not the same process. Breathing moves air; respiration releases energy from food in cells. Using respiration to mean breathing in an answer that compares them loses the definition marks.
A second trap. Writing carbon dioxide as a product of anaerobic respiration in human muscles. Muscle cells produce only lactic acid; carbon dioxide is released only in alcoholic fermentation.
Did you know
How does the body adapt after a few days high in the mountains?
People who travel to a high Himalayan town often feel breathless and tired on the first day, but after several days they find they can walk and climb far more comfortably. The air has not changed. Their blood has.
The kidneys act as oxygen sensors. When the blood reaching them carries less oxygen than usual, cells in the kidneys release a hormone into the blood. That hormone travels to the red bone marrow — the factory where red blood cells are made — and tells it to produce more.
Over the following days and weeks:
- The number of red blood cells in the blood rises
- The total amount of haemoglobin increases
- Each litre of blood can therefore carry more oxygen, making up for the thinner air
Other changes help too. Breathing becomes deeper, more tiny blood vessels can grow in the muscles, and cells become better at using the oxygen they receive.
This natural process explains a common piece of sports advice. Athletes sometimes train at high altitude before important events. They return to lower ground with blood that carries extra oxygen, which can give them more stamina for a while — until the body gradually readjusts to the richer air.
The same response also explains a finding in blood tests. People who have lived for a long time at high altitude often have naturally higher red blood cell counts than people living near the coast — a raised count that is a healthy adaptation, not a disease — which links directly to the blood cell conditions described in the circulatory system chapter.
And it shows how the systems of the body work together. The respiratory system brings in the oxygen, the circulatory system carries it, the kidneys sense its shortage, and the bone marrow responds — four parts of the body cooperating to solve a problem caused simply by climbing a mountain.
The kidneys act as oxygen sensors. When the blood reaching them carries less oxygen than usual, cells in the kidneys release a hormone into the blood. That hormone travels to the red bone marrow — the factory where red blood cells are made — and tells it to produce more.
Over the following days and weeks:
- The number of red blood cells in the blood rises
- The total amount of haemoglobin increases
- Each litre of blood can therefore carry more oxygen, making up for the thinner air
Other changes help too. Breathing becomes deeper, more tiny blood vessels can grow in the muscles, and cells become better at using the oxygen they receive.
This natural process explains a common piece of sports advice. Athletes sometimes train at high altitude before important events. They return to lower ground with blood that carries extra oxygen, which can give them more stamina for a while — until the body gradually readjusts to the richer air.
The same response also explains a finding in blood tests. People who have lived for a long time at high altitude often have naturally higher red blood cell counts than people living near the coast — a raised count that is a healthy adaptation, not a disease — which links directly to the blood cell conditions described in the circulatory system chapter.
And it shows how the systems of the body work together. The respiratory system brings in the oxygen, the circulatory system carries it, the kidneys sense its shortage, and the bone marrow responds — four parts of the body cooperating to solve a problem caused simply by climbing a mountain.
Exam relevance
How does gas transport and respiration appear in NEET Biology?
This is foundation work for Class 11 Breathing and Exchange of Gases and Respiration in Plants, both part of NEET Biology.
Where gas transport leads. Class 11 Breathing and Exchange of Gases explains the transport of oxygen and carbon dioxide through partial pressures and the oxygen dissociation curve, which shows how much oxygen haemoglobin holds at different oxygen levels. The percentages carried in each form, and the role of carbonic anhydrase, are standard NEET facts, and questions ask how factors such as carbon dioxide, acidity and temperature affect oxygen release in the tissues.
Where tissue respiration leads. Class 11 Respiration in Plants breaks cellular respiration into glycolysis, the formation of acetyl coenzyme A, the Krebs cycle and the electron transport system, and counts the ATP formed at each stage. The overall equation and the contrast between aerobic and anaerobic yields introduced here are the starting point for those questions.
Where anaerobic respiration leads. The same chapter describes fermentation — alcoholic in yeast and lactic acid in muscle — and compares their products and energy yields. The ratio of carbon dioxide released to oxygen used, called the respiratory quotient, is also examined, and its value depends on the food substance being respired.
Where oxygen shortage leads. Breathing and Exchange of Gases describes how breathing is regulated by centres in the brain, which respond mainly to the levels of carbon dioxide and hydrogen ions in the blood.
Question types to expect. At this level: transport of gases, breathing versus respiration, anaerobic equations and effects of altitude. In NEET: dissociation curve interpretation, transport percentages, stages and ATP yield of respiration, fermentation products, respiratory quotient, and regulation of breathing, often as statement or match-the-column questions.
The single trap that costs marks. Treating the products of the two kinds of fermentation as the same. Yeast gives ethanol and carbon dioxide; muscle gives lactic acid and no carbon dioxide — and options that mix them are common.
A second trap. Thinking that carbon dioxide is carried mainly by haemoglobin. Most is carried as hydrogen carbonate ions in the plasma, with only a smaller share bound to haemoglobin.
Board versus competitive emphasis. The ICSE paper marks descriptive comparisons, balanced equations and definitions; NEET marks quantitative facts, stages and interpretation of graphs. The transferable habit is tracking each gas and each product to exactly where it is formed and carried.
Where gas transport leads. Class 11 Breathing and Exchange of Gases explains the transport of oxygen and carbon dioxide through partial pressures and the oxygen dissociation curve, which shows how much oxygen haemoglobin holds at different oxygen levels. The percentages carried in each form, and the role of carbonic anhydrase, are standard NEET facts, and questions ask how factors such as carbon dioxide, acidity and temperature affect oxygen release in the tissues.
Where tissue respiration leads. Class 11 Respiration in Plants breaks cellular respiration into glycolysis, the formation of acetyl coenzyme A, the Krebs cycle and the electron transport system, and counts the ATP formed at each stage. The overall equation and the contrast between aerobic and anaerobic yields introduced here are the starting point for those questions.
Where anaerobic respiration leads. The same chapter describes fermentation — alcoholic in yeast and lactic acid in muscle — and compares their products and energy yields. The ratio of carbon dioxide released to oxygen used, called the respiratory quotient, is also examined, and its value depends on the food substance being respired.
Where oxygen shortage leads. Breathing and Exchange of Gases describes how breathing is regulated by centres in the brain, which respond mainly to the levels of carbon dioxide and hydrogen ions in the blood.
Question types to expect. At this level: transport of gases, breathing versus respiration, anaerobic equations and effects of altitude. In NEET: dissociation curve interpretation, transport percentages, stages and ATP yield of respiration, fermentation products, respiratory quotient, and regulation of breathing, often as statement or match-the-column questions.
The single trap that costs marks. Treating the products of the two kinds of fermentation as the same. Yeast gives ethanol and carbon dioxide; muscle gives lactic acid and no carbon dioxide — and options that mix them are common.
A second trap. Thinking that carbon dioxide is carried mainly by haemoglobin. Most is carried as hydrogen carbonate ions in the plasma, with only a smaller share bound to haemoglobin.
Board versus competitive emphasis. The ICSE paper marks descriptive comparisons, balanced equations and definitions; NEET marks quantitative facts, stages and interpretation of graphs. The transferable habit is tracking each gas and each product to exactly where it is formed and carried.
Key takeaways
What must you be able to do from this part?
Two gases carried, two kinds of respiration compared, two anaerobic routes and three oxygen-shortage terms.
- Oxygen: about carried by haemoglobin as oxyhaemoglobin, about dissolved; in lungs, reversed in tissues
- Carbon dioxide: mostly as hydrogen carbonate ions via carbonic anhydrase, partly as carbaminohaemoglobin, some dissolved
- Carbon monoxide binds haemoglobin strongly as carboxyhaemoglobin and blocks oxygen transport
- ** of blood** delivering per gives of oxygen
- Breathing: physical movement of air, in lungs, uses energy, no enzymes
- Tissue respiration: chemical oxidation of glucose in cells, releases energy, many enzymes
- Aerobic respiration: , about ATP
- **About of the energy is stored in ATP; the rest is heat, which keeps the body warm
- Alcoholic fermentation in yeast and plants: glucose to ethanol and CO2
- Lactic acid formation in muscles: glucose to lactic acid, no CO2
- Anaerobic respiration** gives about ATP — aerobic gives times more
- Oxygen debt: extra breathing after exercise to remove lactic acid
- High altitude: lower pressure, fewer oxygen molecules per breath, faster breathing and heart rate, more red blood cells over time
- Hypoxia: shortage of oxygen reaching tissues; asphyxiation: suffocation from oxygen being cut off
The sharpest self-test is one glucose molecule on two paths. Follow it through aerobic respiration in a resting muscle and through anaerobic respiration in a sprinting muscle, naming the products, the ATP gained and where the carbon ends up — then explain why the sprinter keeps panting after stopping.
- Oxygen: about carried by haemoglobin as oxyhaemoglobin, about dissolved; in lungs, reversed in tissues
- Carbon dioxide: mostly as hydrogen carbonate ions via carbonic anhydrase, partly as carbaminohaemoglobin, some dissolved
- Carbon monoxide binds haemoglobin strongly as carboxyhaemoglobin and blocks oxygen transport
- ** of blood** delivering per gives of oxygen
- Breathing: physical movement of air, in lungs, uses energy, no enzymes
- Tissue respiration: chemical oxidation of glucose in cells, releases energy, many enzymes
- Aerobic respiration: , about ATP
- **About of the energy is stored in ATP; the rest is heat, which keeps the body warm
- Alcoholic fermentation in yeast and plants: glucose to ethanol and CO2
- Lactic acid formation in muscles: glucose to lactic acid, no CO2
- Anaerobic respiration** gives about ATP — aerobic gives times more
- Oxygen debt: extra breathing after exercise to remove lactic acid
- High altitude: lower pressure, fewer oxygen molecules per breath, faster breathing and heart rate, more red blood cells over time
- Hypoxia: shortage of oxygen reaching tissues; asphyxiation: suffocation from oxygen being cut off
The sharpest self-test is one glucose molecule on two paths. Follow it through aerobic respiration in a resting muscle and through anaerobic respiration in a sprinting muscle, naming the products, the ATP gained and where the carbon ends up — then explain why the sprinter keeps panting after stopping.